Previous work in our laboratory has demonstrated that the paclitaxel induced initial phase of apoptosis in a variety of cell lines including MCF-7 breast cancer cells and BR ovarian cells is mediated through a Ras/Rac/Ask1/JNKK/JNK signal transduction pathway. However, the second phase of paclitaxel action is not prevented by blockade of this pathway. Recent studies on MCF-7 cells and a variety of other cell types suggests that estrogens can inhibit apoptosis, more specifically, data indicates a possible interaction between paclitaxel and estrogens in regulating apoptosis in breast cancer cells. Several studies also suggest that antiestrogens have apoptotic effects in ER positive breast Ca cells. We have accumulated preliminary evidence confirming an anti-apoptotic role for estrogens in MCF-7 cells. However, the mechanisms of estrogen action as an anti-apoptotic agent or their potential interactions with pro-apoptotic agents such as paclitaxel are totally unknown. Elucidations of these interactions is particularly significant since estrogens and microtubule interfering agents (MIAs) such as paclitaxel have clinically established roles in promotion and therapy of breast and ovarian cancer respectively. We propose that estrogens can act as anti-apoptotic agents because of their ability to regulate the Ras/Rac-JNK pathway and the Cdk/cyclin/Cdk inhibitor activity in breast and ovarian cancer cells. We have proposed the following Specific Aims to test this broad hypothesis. Specific Aim 1: Determine the role of Cdks in the apoptotic action of paclitaxel in MCF-7 and BR and BG1 (ovarian) cancer cells with the intention of elucidating the role of the cell cycle, if any, in paclitaxel action. Specific Aim 2: Analyze the putative interactions between paclitaxel and estradiol in regulating apoptosis in the above cell lines. Experiments will be designed to elucidate interaction of estrogens with the Ras/Rac/JNKK/JNK/AP1 pathway activated by paclitaxel. Specific Aim 3: Given the fact that estrogens can regulate the activity of several genes which can modulate apoptosis, we will determine potential role of c-myc, Bc12, p53, p300/CBP Akt in the anti apoptotic effects of estradiol using overexpression of wild type and dominant negative (DN) versions of the genes of interest.